1. Field of the Invention
This invention relates to an eye refractive power measuring apparatus.
2. Related Background Art
As an ophthalmologic instrument for effecting the observation or measurement of an examinee's eye, for example, an eye refractive power measuring apparatus for automatically measuring the examinee's eye refractive power is known under the name of an auto refractometer, and is described in U.S. Pat. No. 4,353,625 and Japanese Patent Application Laid-Open No. 62-5147. This measuring apparatus measures the eye refractive power when the optical axis of the examinee's eye and the optical axis of the measuring apparatus coincide with each other. The direction of the astigmatism axis (cylindrical axis) of the eye to be examined is also measured as part of the eye refractive power. The direction of the astigmatism axis is represented by coordinates with the eye to be examined as the reference.
Generally, the measuring part of this measuring apparatus is placed on a sliding stand movable right and left and back and forth, with a view to measure right and left eyes. In this case, discrimination as to which of the right and left eyes is being measured has been effected by obtaining information indicating whether the measuring part is on the right or left side of the sliding stand.
Recently, demand has been strong for measuring the eye refractive power during various operations, and compact and manually holdable eye refractive power measuring apparatuses have been introduced. However, when the apparatus becomes manually holdable, it becomes impossible to discriminate between right and left eyes based on the position of the measuring part on the sliding stand, as has heretofore been done.
As a manually holdable apparatus capable of discriminating between right and left eyes, there is an eye examining apparatus described in Japanese Patent Application Laid-Open No. 4-73046. This apparatus is provided with a light source emitting a beam of light for illuminating the sideways part of an eye to be examined, and a photoelectric sensor for receiving the reflected light of said beam of light, and discriminates between right and left eyes.
This eye examining apparatus, however, can measure only from a certain predetermined direction relative to the eye to be examined. For example, when an examinee is to be measured while lying down on a bed or the like in a hospital, the measuring apparatus is unavoidably used from the bed side and necessarily, the apparatus is used in opposed relationship with the eye to be examined from various directions.
Usually, when the direction of the astigmatism axis is to be measured, the direction of the astigmatism axis is measured on coordinate system with the measuring apparatus as the reference.
Accordingly, when the measuring apparatus is used in various directions relative to the eye to be examined, the coordinate system with the eye to be examined as the reference and the coordinate system with the measuring apparatus as the reference do not coincide with each other in some cases. At such time, the actual direction of the astigmatism axis on the coordinate system with the eye to be examined as the reference and the direction of the astigmatism axis on the coordinate system with the measuring apparatus as the reference deviate from each other.